1. Field of the Invention
The present invention relates to a method of manufacturing multiple kinds of products in an arbitrarily selected order (in a mixed order) in one manufacturing apparatus by combining, through welding, a plurality of parts belonging to each of the multiple kinds of products, such as floors of multiple kinds of motor vehicles.
2. Description of Related Art
Conventionally, a floor of a motor vehicle is assembled by combining, through welding, a front component which constitutes an engine room, a front floor which constitutes a floor section of a vehicle compartment, and a rear floor which constitutes a floor section of a trunk portion.
In manufacturing the floor of a motor vehicle, the following steps are conventionally taken. Namely, in each of the assembly lines for assembling therein the front component, the front floor, and the rear floor, respectively, the welding of all of the welding points of a plurality of constituting members which constitute each of the parts is performed, whereby each of the parts is assembled. Then, the assembled front component, the front floor, and the rear floor are tack-welded to thereby assemble the floor. Thereafter, in a reinforce-welding line, the reinforce-welding is performed to the connecting portions among the parts.
The required number of welding points which are required for assembling each of the parts, such as the front component, the front floor, and the rear floor, varies with the kind (or type) of the vehicle. Therefore, in the conventional method in which all of the welding points of each of the parts are welded in the respective assembly lines, the following becomes necessary. Namely, when the vehicle floors for multiple kinds of vehicles are manufactured in an arbitrarily selected order in one manufacturing apparatus, the number of welding robots to be disposed in each of the part assembly lines must be decided based on that part of the kind of vehicle which has the largest number of welding points. As a result, when the kind of the vehicle which has a smaller number of welding points is being manufactured, the availability factor (or the rate of operation) of the welding robots becomes smaller. When a new kind of vehicle which has a larger number of welding points is introduced into the manufacturing apparatus, the respective part assembly lines must be modified. As a result, the cost for equipment investment becomes large and the time for modification is required. They become a hindrance to the improvement in the productivity.
In view of the above points, the present invention has an object of providing a method of manufacturing multiple kinds of products in an arbitrarily selected order in one manufacturing apparatus, in which the rate of operation of the welding robots is improved and the cost for equipment investment at the time of introducing a new kind of vehicle into the manufacturing apparatus is reduced.
In order to attain the above and other objects, the present invention is a method of manufacturing multiple kinds of products in an arbitrarily selected order in one manufacturing apparatus by combining, through welding, a plurality of parts belonging to each of the multiple kinds of products, the method comprising the steps of: combining, through welding, a plurality of members constituting the parts in a part assembly line which is prepared for each of the parts to thereby assemble each of the parts; tack-welding the plurality of parts to thereby assemble the products; and thereafter reinforce-welding the products in a reinforce-welding line, wherein a number of welding points of each of the parts in each of the part assembly lines is made equal to one another for all of the multiple kinds of products, and wherein those welding points of each of the parts which fall short of a required number of welding points are welded in the reinforce-welding line.
According to the present invention, the number of welding points of each of the parts in each of the part assembly lines does not vary with different kinds of the products. Therefore, the rate of operation of the welding robots disposed in each of the part assembly lines does not become lower even when the kind of the product changes. In addition, when a new kind of product, whose parts have a larger number of welding points than the parts of the existing kind of product have, is introduced into the manufacturing apparatus, it is sufficient to modify only the reinforce-welding line, and the modification to each of the part assembly lines is not required any more. Further, the welding points of a plurality of parts in the reinforce-welding line can be performed by the common welding robots. Therefore, as compared with the arrangement in which the number of welding robots is increased in each of the part assembly lines, the number of increase in the welding robots may be smaller. As a result, the cost of equipment investment at the time of newly introducing a new kind of product into the manufacturing apparatus, can be reduced and the time therefor can also be shortened.